There obviously needs to be a way to wire the arcade controls to the computer, and there are a number of choices. One way to do it is to buy a dedicated interface device, such as those offered by Hagstrom Electronics. If I build another case in the future, I'll probably go this route. But for this project, I decided to hack an interface based on another input device, such as a joystick or keyboard.
Logitech USB Joystick This section is a bit lengthy, mainly because it describes my multiple failed attempts to find something to use to hook the controls into the computer. The real stuff is at the bottom; I'm including all of the failures in the hopes that it'll inform others and save them some work My first plan was to hack a USB joystick, such as the Logitech Dual Action Gamepad USB Joystick shown at right. There are seven screws on the bottom, including one that was hidden by the quality check sticker. Removing these let me open up the joystick case.
When I got inside, yikes!
I was hoping to be able to simply find a few points where I could solder
some wires leading to the buttons, but I couldn't readily find any.
Ummm, where? I wanted to solder the microswitches that are in the joystick and buttons in parallel with switches in the joystick, but I couldn't decide how to do that. All of the points were so small, it seemed that it would be quite difficult to solder anything on. The bottom side of the joystick circuit board wasn't any better; there weren't any clearly good places to solder any leads.
Gateway Keyboard, Apart Since the joystick looked a bit tough to work with, the next logical choice would be a keyboard. I have several old keyboards lying around, so I grabbed a PS/2 one that would work with the PS/2 input on the computer. It was a soft-touch (no clicky keys) Gateway keyboard, which opened easily enough.
Unfortunately, it wasn't going to be easy to hack this, either. There was a plastic membrane with contacts "printed" onto it, and it worked a lot like the USB joystick. I couldn't solder anything onto the plastic, of course, beacuse the heat from the soldering iron would have melted it immediately. MAYBE I could have used the small circuit board that made contact with the plastic, and run leads off of it. But I didn't want to have to "hack the matrix" that the keyboard used to scan the keys for which ones were depressed. By now, I was a little bit depressed myself.
Opening the IBM Keyboard So I turned my attention towards an older IBM keyboard that I have. This one has clicky keys (due to switches inside?) and a PS/2 connector, which seemed to make it a good choice. I needed to loosen a few screws on the bottom and then pry it open with a screwdriver.
Opening the IBM Keyboard But when I did, over 100 springs poured out of the case! Despite the clicking sound it makes when you press a key, this keyboard didn't have any switches inside, either.
It's an interesting design, to say the least. When the spring inside a key is compressed, it deforms, and smacks the side of the key housing. That's what makes the clicking sound when you press a key - not a switch. So, unfortunately, there wasn't anything inside this keyboard that I could solder leads to, either.
Old Microswitch Keyboard I had to go back to a keyboard from my old 90 MHz Pentium, circa 1994. It's got microswitches inside, and an AT connector. I could use it, thankfully, because each switch has two pins that are soldered to the main circuit board. All I'd have to do is to solder the leads for each switch to the pins on the bottom of the circuit board. I'd also have to get an AT-to-PS/2 adapter, which was easy enough to find online (I couldn't find any in my stash of random adapters).
Hacked Keyboard To solder the leads to the keyboard, I found that the easiest thing to do was to tin each lead (melt some solder onto it) and then solder it to the bottom of the circuit board, melting the existing solder on the board with the soldering iron while pressing the tinned lead into it. Using stranded copper wire, not solid, made it easier to tin the leads, since the stranded wire "soaks up" the solder very easily. It's also more flexible, which makes it easier to route and manipulate when installing the components into the cabinet.
Keyboard Mount Panel Once the keyboard had wires soldered to it, it needed to be mounted inside the cabinet. I cut a plywood panel and screwed two 1x2 pieces of poplar to it, then screwed the keyboard circuit board to the 1x2s, using the existing screw holes in the circuit board. Using 1x2s left a good 1.5" of room between the circuit board and the plywood for the wires to come out without being too stressed.
Keyboard Mounted I should also include a table that shows the keys to which I connected the controls. As I recall, the joystick was connected to the arrow keys, the fire buttons were connected to Enter and Shift, the one- and two-player buttons were connected to 1 and 2, the coin acceptors were connected to 5 and 6, reset was connected to Escape, and the pause button was connected to... the knee bone? Hopefully any software you use will let you re-map the key assignments. I also screwed another piece of 1x2 into the plywood to hold the leads in place. This is to help make sure they aren't ripped off of the circut board in case they're pulled on during installation, or later on, say, when the coin door is opened. One thing that's not shown in this photo is that I later stapled the cable running to the circuit board to the plywood using an electric staple gun. Again, this is to help relieve any stress on the cable.
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